DESCRIPTION: This research project proposes to use positional cloning to identify the gene(s) that is (are) responsible for the development of certain sub-sets of hereditary osteoarthritis characterized by the deposition of calcium pyrophosphate in disease-prone joints (CPPDD). Despite ambiguous clinical presentation, it has been estimated a prevalence of 1 in 1000 in patients with crystal-induced inflammation, and a prevalence as high as 30-60% in elderly patients with crystal deposition secondary to sever osteoarthritis. Hence, the investigation of the etiology of familial CPPDD allows a unique opportunity to define molecularly pathologic mechanisms that initiate and/or coincide with crystal-associated arthropathy. Toward this end, the following aims are proposed: (1) fine linkage mapping of the CPPDD locus at chromosomal interval 5p15 previously identified in a large Argentinean kindred will be undertaken to narrow the disease gene interval to within 1 cM; (2) use of appropriate polymorphic markers and YAC clones to physically define the region of the CPPDD disease gene interval; cosmids selected by hybridization to the YACs of interest will be used to recover expressed sequences within the interval; (3) identification of expressed sequences recovered by exon trapping or cDNA selection which, after being assessed for tissue-specific expression, will be used to isolate overlapping cDNA clones from tissue-specific cDNA libraries; and (4) search for dominant mutations potentially responsible for the disease phenotype using the positive cDNA clones.